[3.13] gh-123091: Use more _Py_IsImmortalLoose() (GH-123602) (GH-123622)

Switch more _Py_IsImmortal(...) assertions to _Py_IsImmortalLoose(...)

The remaining calls to _Py_IsImmortal are in free-threaded-only code,
initialization of core objects, tests, and guards that fall back to
code that works with mortal objects.

(cherry picked from commit 57c471a6880956338549380fc5fb35c986937901)